Effect of off-zenith observations on reducing the impact of precipitation on ground-based microwave radiometer measurement accuracy
作者单位：Hubei Key Laboratory for Heavy Rain Monitoring and Warning Research Institute of Heavy Rain China Meteorological Administration Radiometrics 4909 Nautilus Court North Boulder CO USA Wuhan Meteorological Bureau of Hubei Province
会议名称：《第31届中国气象学会年会》
会议日期：2014年
学科分类：07[理学] 070601[理学-气象学] 0706[理学-大气科学]
基 金：supported by the National High Technology Research and Development Program (“863” Program) of China (Grant No. 2012AA120902) the open project of State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences (Grant No. 2013LASW-A02) the National Natural Science Foundation of China (Grant Nos. 41175016 and 41375041)
关 键 词：microwave radiometer off-zenith observation precipitation accuracy
摘 要：Microwave radiometers(MWR) can be useful for the detection of mesoscale phenomena because they provide thermodynamic profiles in a minute time scale. These profiles are mainly used in non-precipitation conditions due to degraded accuracy of the MWR measurements in precipitation. Recently, Radiometrics Corporation used proprietary neural network methods to retrieve temperature, humidity and liquid profiles from off-zenith(15° elevation) radiometer observations to provide higher accuracy during precipitation. In this paper, using the MWR-retrieved temperature and humidity profiles with collocated radiosondes from June 2010 to September 2013 in Wuhan, the impact of precipitation on the MWR measurement accuracy as well as the effect of off-zenith neural network methods on it is investigated. In precipitation, the correlation coefficients of the MWR temperature and vapour density profiles against radiosondes are smaller than that in non-precipitation, and the bias and RMS against radiosondes also increase, especially around 2 km heights. For the MWR relative humidity profile, the correlation coefficient in precipitation is obvious smaller than that in non-precipitation below 4.5 km, and the bias and RMS against radiosondes are clearly larger above 5.5 km. Moreover, the differences between the precipitation and non-precipitation cases mostly are statistically significant. Compared with the results of the zenith observation, the off-zenith observation makes a positive effect on reducing the impact of precipitation on the accuracy of MWR temperature and vapour density retrievals. On the whole, the MWR temperature bias and RMS against radiosondes in precipitation are reduced from 3.6 and 4.2 K to 1.3 and 3.1 K, respectively, and the MWR vapour density bias is also reduced from 1.10 g/m3 to 0.18 g/m3 with the RMS decreasing from 2.90 g/m3 to 1.91 g/m3. The temperature correlation coefficient between the MWR and radiosonde in precipitation is clearly improved above 3 km height